Septoria Tritici Blotch Severity Research Articles

Genome-wide association study for resistances to yellow rust, powdery mildew, and Septoria tritici blotch in cultivated emmer

Emmer is a progenitor of bread wheat and evolved in the Levant together with the yellow rust (YR), powdery mildew (PM) fungi, and a precursor of Zymoseptoria tritici causing Septoria tritici blotch (STB). We performed a genome-wide association mapping for the three disease resistances with 143 cultivated emmer accessions in multi-environmental trials. Significant (P < 0.001) genotypic variation was found with high heritabilities for the resistances to the two biotrophs and a moderate heritability for STB resistance. For YR, PM, and STB severity nine, three, and seven marker-trait associations, respectively, were detected that were significant across all environments. Most of them were of low to moderate effect, but for PM resistance a potentially new major gene was found on chromosome 7AS. Genomic prediction abilities were high throughout for all three resistances (≥ 0.8) and decreased only slightly for YR and PM resistances when the prediction was done for the second year with the first year as training set (≥ 0.7). For STB resistance prediction ability was much lower in this scenario (0.4). Despite this, genomic selection should be advantageous given the large number of small QTLs responsible for quantitative disease resistances. A challenge for the future is to combine these multiple disease resistances with better lodging tolerance and higher grain yield.

Improved control of septoria tritici blotch in durum wheat using cultivar mixtures

AbstractMixtures of cultivars with contrasting levels of resistance can suppress infectious diseases in wheat, as demonstrated in numerous field experiments. Most studies focus on airborne pathogens in bread wheat, while splash‐dispersed pathogens have received less attention, and no studies have been conducted in durum wheat. We conducted a 2‐year field experiment in Tunisia to evaluate the performance of cultivar mixtures with varying proportions of resistance (0%–100%) in controlling the polycyclic, splash‐dispersed disease septoria tritici blotch (STB) in durum wheat. To measure STB severity, we used a high‐throughput method based on digital image analysis of 3,074 infected leaves collected from 42 and 40 experimental plots during the first and second years, respectively. This allowed us to quantify pathogen reproduction on wheat leaves and to acquire a large data set that exceeds previous studies with respect to accuracy and precision. Our analyses show that introducing only 25% of a disease‐resistant cultivar into a pure stand of a susceptible cultivar provides a substantial reduction of almost 50% in disease severity compared to the susceptible pure stand. However, incorporating two resistant cultivars instead of one did not further improve disease control, contrary to predictions of epidemiological theory. Susceptible cultivars can be agronomically superior to resistant cultivars or be better accepted by growers for other reasons. Hence, if mixtures with only a moderate proportion of the resistant cultivar provide a similar degree of disease control as resistant pure stands, as our analysis indicates, such mixtures are more likely to be accepted by growers.

Control of Septoria tritici blotch by winter wheat cultivar mixtures: Meta-analysis of 19 years of cultivar trials

Wheat is the most commonly grown cereal crop in Europe and in major parts of Europe the most yield limiting disease is Septoria tritici blotch (STB) caused by Zymoseptoria tritici. Currently, the control of the disease depends on cultivar resistance and substantial input of fungicides. The impact of using mixtures of elite cultivars as an alternative was investigated through a meta-analysis based on trial data from the Danish national cultivar testing. The cultivar testing includes a four-way cultivar mixture every year and in these trials STB severity and yield have been monitored at multiple locations between 1995 and 2017. Results from 19 years of cultivar testing trials provided a data set for 406 trials from which the effect of mixtures was evaluated. The meta-analysis revealed that cultivar mixtures reduced STB severity with 10.6% and increased yields with 1.4% across all trials. The effects were greatest in untreated trials where STB severity was reduced with 17% and yields increased with 2.4%. The mixtures did not only perform better than the average of their component cultivars grown as pure stand, they also performed better than the average of the four most grown cultivars in a given year. No relationship was found between disease pressure or location and the performance of the mixtures. The mixtures included in the cultivar testing were not designed to control STB and the results are therefore perceived as a baseline to the attainable disease control from mixtures. The use of cultivar mixtures is relevant for low input farming systems, but can also contribute to disease control in intensive farming systems. Cultivar mixtures have the potential to minimise dependency on fungicides as an important element in integrated pest management.

GWAS-Assisted Genomic Prediction to Predict Resistance to Septoria Tritici Blotch in Nordic Winter Wheat at Seedling Stage.

Septoria tritici blotch (STB) disease caused by Zymoseptoria tritici is one of the most damaging diseases of wheat causing significant yield losses worldwide. Identification and employment of resistant germplasm is the most cost-effective method to control STB. In this study, we characterized seedling stage resistance to STB in 175 winter wheat landraces and old cultivars of Nordic origin. The study revealed significant (p < 0.05) phenotypic differences in STB severity in the germplasm. Genome-wide association analysis (GWAS) using five different algorithms identified ten significant markers on five chromosomes. Six markers were localized within a region of 2 cM that contained seven candidate genes on chromosome 1B. Genomic prediction (GP) analysis resulted in a model with an accuracy of 0.47. To further improve the prediction efficiency, significant markers identified by GWAS were included as fixed effects in the GP model. Depending on the number of fixed effect markers, the prediction accuracy improved from 0.47 (without fixed effects) to 0.62 (all non-redundant GWAS markers as fixed effects), respectively. The resistant genotypes and single-nucleotide polymorphism (SNP) markers identified in the present study will serve as a valuable resource for future breeding for STB resistance in wheat. The results also highlight the benefits of integrating GWAS with GP to further improve the accuracy of GP.

Management of Septoria Tritici Blotch (&amp;lt;i&amp;gt;Septoria tritici&amp;lt;/i&amp;gt;) of Bread Wheat (&amp;lt;i&amp;gt;Triticum aestivum&amp;lt;/i&amp;gt; L.) in the Central Highlands of Ethiopia

Septoria tritici blotch (STB) is an economically important foliar disease in the major wheat-growing areas of Ethiopia. The current research was conducted to determine the impact of wheat varieties and fungicides on disease development and wheat yield. Besides, the effect of bread wheat varieties and fungicides on STB development, wheat yield was evaluated at Holleta and Kulumsa in a factorial field experiment involving three bread wheat varieties and six fungicide spray schedules. At Holetta, variety Kekeba had the highest AUDPC (2548) value followed by Madawalabu and Alidoro; whereas at Kulumsa the highest AUDPC (1509) was recorded on variety Madawalabu followed by Alidoro and Kekeba varieties. STB incidence and severity were significantly reduced by the application of fungicides across varieties but fungicide-variety combinations had differential effects on disease development. Wheat grain yields were the lowest from unsprayed plots regardless of variety and location. Kekeba variety treated with Mancozeb-Tilt-Mancozeb-Tilt (MTMT) fungicide combination produced the highest yield (5.05t/ha). The highest (577.31%) and lowest (-19.95%) marginal rate of return were obtained from Tilt and MTMT sprayed fields at Holetta planted with Kekeba and Madawalabu varieties, respectively. On the other hand, at Kulumsa, the highest marginal rate of return (886.88%) and the lowest marginal rate of return (-63.98%) was obtained from Tilt and Mancozeb sprays on Madawalabu and Alidoro varieties, respectively. The present findings confirmed the importance of STB in Ethiopia and the role fungicides play in managing the disease on partially resistant varieties.

Accuracy of within- and among-family genomic prediction for Fusarium head blight and Septoria tritici blotch in winter wheat.

Genomic selection is an approach that uses whole-genome marker data to predict breeding values of genotypes and holds the potential to improve the genetic gain in breeding programs. In this study, two winter wheat populations (DS1 and DS2) consisting of 438 and 585 lines derived from six and eight bi-parental families, respectively, were genotyped with genome-wide single nucleotide polymorphism markers and phenotyped for Fusarium head blight and Septoria tritici blotch severity, plant height and heading date. We used ridge regression-best linear unbiased prediction to investigate the potential of genomic selection under different selection scenarios: prediction across each winter wheat population, within- and among-family prediction in each population, and prediction from DS1 to DS2 and vice versa. Moreover, we compared a full random model to a model incorporating quantitative trait loci (QTL) as fixed effects. The prediction accuracies obtained by cross-validation within populations were moderate to high for all traits. Accuracies for individual families were in general lower and varied with population size and genetic architecture of the trait. In the among-family prediction scenario, highest accuracies were achieved by predicting from one half-sib family to another, while accuracies were lowest between unrelated families. Our results further demonstrate that the prediction accuracy can be considerably increased by a fixed effect model approach when major QTL are present. Taken together, the implementation of genomic selection for Fusarium head blight and Septoria tritici blotch resistance seems to be promising, but the composition of the training population is of utmost importance.

Occurrence of Septoria tritici blotch (Zymoseptoria tritici) disease on durum wheat, triticale, and bread wheat in Northern Tunisia.

Wheat (Triticum aestivum L.) is the most important cereal crop in Tunisia, nonetheless production is highly affected by drought and diseases mainly Septoria tritici blotch (STB) caused by Zymoseptoria tritici (Roberge ex Desm.) Quaedvl. & Crous anamorph and Mycosphaerella graminicola (Fuckel) J. Schrot. 1894 teleomorph; that has become an inherent disease of durum wheat (Triticum turgidum L. subsp. durum (Desf.) van Slageren) but rarely observed on bread wheat (Triticum aestivum L. subsp. aestivum) and on triticale (×Triticosecale spp.) The main objective of this work was to study the prevalence and geographical distribution of Z. tritici on triticale, durum wheat and particularly on bread wheat in different cereal growing regions of North and Northwestern Tunisia to confirm its presence/absence on bread wheat. For this study, 126 wheat fields were surveyed in North and Northwestern Tunisia during 2015-2016 and 2016-2017 cropping seasons. STB on durum wheat was present in the majority of inspected durum wheat fields, where high mean incidence (60%) and severity (40%) were recorded at Jendouba, Bizerte, Beja, and Kef. The survey data revealed low risk on bread wheat with an incidence of 23% and 29% at Bizerte and Beja, respectively. However high incidence of 84% and 52% was recorded at Cap Bon in 2016 and 2017, respectively and mainly at El Haouaria where STB severity was relatively high on bread wheat landrace of unknown origin but called by local farmers as ‘Farina arbi’. Sporadic incidence was recorded on Triticale of 100% at Jendouba (in 2016), and 33% at Bizerte (in 2016 and 2017) and absence at all other surveyed sites; likewise for severity at same locations where 13% and 42% were recorded in 2016. The survey data revealed low risk on bread wheat except at El Haouaria where STB severity was relatively high on a bread wheat landrace; while it was considered as high risk at all durum wheat fields in Beja, Bizerte, Jendouba, Zaghouan and Kef regions, such distinct occurrence could lead to clarify host specificity in Z. tritici.

The effect of fungicides applied pre-stem extension on septoria tritici blotch and yield of winter wheat in Ireland

Ireland has the potential to produce some of the highest winter wheat yields in the world, however due to the highly disease conducive environment fungicides are heavily relied upon to achieve these yields. These fungicides primarily target control of septoria tritici blotch (STB), which if left untreated can result in significant reductions in yield. Typically winter wheat fungicide programmes are comprised of four applications, the first of which is applied pre-stem extension (PSE). It has been suggested that applying fungicides at this stage in the crops development slows disease progression to the upper canopy (final leaves three, two and one) which is responsible for the majority of yield potential. This study tested the effect of different pre-stem extension fungicide treatments on STB severity in the upper canopy during grain filling and subsequent grain yield in field trials conducted at three Irish locations over three consecutive growing seasons (2012-2014). When applied as part of a typical foliar fungicide programme significant differences in levels of STB on the final leaf three were observed at growth stage GS83between the PSE treatments (P = 0.05), with the solo azole resulting in higher levels of disease compared to the other fungicide treatments. Despite these differences in STB control no significant differences were observed between the treatments in final yield (P = 0.44). This study shows there is no yield advantage to applying fungicides prior to stem extension for control of STB, however, if they are being applied for the control of other disease e.g. yellow rust careful consideration should be taken with regards to choice of fungicide to avoid increasing STB severity later in the season.

Yield and optimum fungicide dose rates for winter wheat (Triticum aestivum L.) varieties with contrasting ratings for resistance to septoria tritici blotch

This study evaluated the effect of varieties of winter wheat that differ in septoria tritici blotch (STB) resistance rating on yield and profit margin obtained when treated with varying application rates of an azole-only fungicide or an azole-plus-SDHI fungicide. Seven field trials were conducted over four growing seasons in the south-east of Ireland, 2012–2015. Each trial consisted of a factorial arrangement of two fungicide types (azole and azole+SDHI), five applications rates (0, 0.25, 0.50, 1.0 and 2.0 times the recommended dosage per application, applied twice during the growing season) and three varieties that differed in reported STB-resistance ratings (5, 7 and 8 on a scale of 0–9; SR5, SR7, SR8). The severity of STB and grain yield were determined and analysed by analysis of variance. The economic optimum rate of each fungicide product was also determined for each variety at each site-season. When untreated, the STB severity was lower for SR8 at GS71 than the other varieties at four of the five evaluated sites, while SR7 incurred lower STB severity than SR5 at only three of the five sites that comparisons were available. The STB severity for the SR8 variety was unaffected by the application rate of either fungicide at most sites. Increased rate of fungicide increased yield, and this effect was generally consistent among the SR5 and SR7 varieties at site-seasons with medium or high STB pressure. However, the yield benefit to increased rate of either fungicide type was minimal for SR8. The variation in the economic optimum rate of either fungicide type evaluated was greater between site-seasons than between the SR5 and SR7 varieties. However, the SR8 variety had a comparatively low economic optimum rate of an azole+SDHI in four of the five site-seasons. When averaged across all site-seasons, the margin above fungicide cost was greater for crops treated with the azole+SDHI treatment than an azole-only treatment for all varieties evaluated. These findings indicate that the range of STB resistance exhibited by the majority of varieties currently grown in Ireland (5–7 on the 0–9 scale) do not consistently confer differences in the optimum fungicide application rate. However the results also suggest that varieties exhibiting strong STB resistance may allow confident reductions to fungicide programs, should they become commonly available in the future.

Response of selected winter wheat cultivars to inoculation with different Mycosphaerella graminicola isolates

Sip V., Chrpova J., Palicova J. (2015): Response of selected winter wheat cultivars to inoculation with different Mycosphaerella graminicola isolates. Czech J. Genet. Plant Breed., 51: 86–95. Five winter wheat cultivars, differing in resistance to Septoria tritici blotch (STB), were spray inoculated under field conditions for two years and at two locations with nine Mycosphaerella graminicola isolates and a mixture of isolates that were obtained from different regions of the Czech Republic. Main aims of this study were (i) to compare isolate, host cultivar and environmental effects on five traits indicative of STB severity and (ii) to analyse pathogen aggressiveness and host-pathogen relations for improving evaluation of cultivar resistance. ANOVA showed in all traits, except the reduction in 1000 grain weight, significant isolate effects. However, the effects of isolate and genotype by isolate interactions were much lower (2.3–4%) than cultivar (19.1–53.7%) and environmental (11.9–58.6%) effects. Cultivar resistance to the disease limited much the loss in grain weight per spike to a halve, from 34.7% in the susceptible Bakfis to 17.3% in the resistant Arina. Visual scoring of symptoms in the middle and at the end of disease development (performed on the 1–9 scale), reflecting the disease progress and infected leaf area, showed the highest cultivar effect (54%) and could be recommended for evaluation of cultivar resistance in breeding practice. All examined traits were significantly interrelated, but significant differences between all the five cultivars were only detected after examination of the % coverage of flag leaves with lesions bearing pycnidia. Resistance in the cultivar Arina was detected by all isolates and the isolate mixture. In spite of significant differences in classification of resistances in the cultivars Bohemia and Mulan after inoculation with one isolate (1081), specific interactions between cultivars and isolates collected in this Central European region are rare. The study leads to a conclusion that investigation into stability of STB resistance across a wide range of environments is more valuable for breeding purposes than the study of cultivar response to different isolates. Combination of important isolate properties in a mixture of isolates is stressed as well

Potential and limits of whole genome prediction of resistance to Fusarium head blight and Septoria tritici blotch in a vast Central European elite winter wheat population.

Fusarium head blight and Septoria tritici blotch resistances are complex traits and can be improved efficiently by genomic selection modeling main and epistatic effects. Enhancing the resistance against Fusarium head blight (FHB) and Septoria tritici blotch (STB) is of central importance for a sustainable wheat production. Our study is based on a large experimental data set of 2325 inbred lines genotyped with 12,642 SNP markers and phenotyped in multi-environmental trials for FHB and STB resistance as well as for plant height. Our objectives were to (1) investigate the impact of plant height on FHB and STB severity, (2) examine the potential of marker-assisted selection, and (3) study the prediction ability of genomic selection modeling main and epistatic effects. We observed low correlations between plant height and FHB (r=-0.15; P<0.05) as well as STB severity (r=-0.17; P<0.05) suggesting negligible morphological resistances. Cross-validation in combination with association mapping revealed absence of large effect QTL impeding an efficient pyramiding of different resistance loci through marker-assisted selection. The prediction ability of genomic selection was high amounting to 0.6 for FHB and 0.5 for STB resistance. Therefore, genomic selection is a promising tool to improve FHB and STB resistance in wheat.

Quantitative Trait Loci for Adult-Plant Resistance to Mycosphaerella graminicola in Two Winter Wheat Populations

Septoria tritici blotch (STB) is one of the most important leaf spot diseases in wheat worldwide. The goal of this study was to detect chromosomal regions for adult-plant resistance in large winter wheat populations to STB. Inoculation by two isolates with virulence to Stb6 and Stb15, both present in the parents, was performed and STB severity was visually scored plotwise as percent coverage of flag leaves with pycnidia-bearing lesions. 'Florett'/'Biscay' and 'Tuareg'/'Biscay', each comprising a cross of a resistant and a susceptible cultivar, with population sizes of 316 and 269 F(7:8) recombinant inbred lines, respectively, were phenotyped across four and five environments and mapped with amplified fragment length polymorphism, diversity array technology, and simple sequence repeat markers covering polymorphic regions of ≈1,340 centimorgans. Phenotypic data revealed significant (P < 0.01) genotypic differentiation for STB, heading date, and plant height. Entry-mean heritabilities (h(2)) for STB were 0.73 for 'Florett'/'Biscay' and 0.38 for 'Tuareg'/'Biscay'. All correlations between STB and heading date as well as between STB and plant height were low (r = -0.13 to -0.20). In quantitative trait loci (QTL) analysis, nine and six QTL were found for STB ratings explaining, together, 55 and 51% of phenotypic variation in 'Florett'/'Biscay' and 'Tuareg'/'Biscay', respectively. Genotype-environment and QTL-environment interactions had a large impact. Two major QTL were detected consistently across environments on chromosomes 3B and 6D from 'Florett' and chromosomes 4B and 6B from 'Tuareg', each explaining 12 to 17% of normalized adjusted phenotypic variance. These results indicate that adult-plant resistance to STB in both mapping populations was of a quantitative nature.

Stability of Adult-plant Resistance to Septoria tritici blotch in 24 European Winter Wheat Varieties Across Nine Field Environments

Septoria tritici blotch (STB) is one of the most important leaf diseases in wheat worldwide. Objectives of this study were (i) to compare inoculation and natural infection ; (ii) to evaluate the level of adult-plant resistance to STB using four isolates; and (iii) to analyse environmental stability of 24 winter wheat (Triticum aestivum L.) varieties in inoculated vs. non-inoculated field trials across 3 years including nine environments (location x year combinations). Field trials were sown in split-plot design inoculated with four aggressive isolates of S. tritici plus one non-inoculated variant as main factor and 24 wheat varieties as subfactor. Septoria tritici blotch severity was visually scored as percentage flag leaves covered with lesions bearing pycnidia. Overall STB rating ranged from 8% (Solitar) to 63% (Rubens) flag leaf area affected, resulting in significant (P < 0.01) genotypic variance. Variance of genotype x environment interaction amounted to approximately 50% of the genotypic variance. Genotype x isolate interaction variance was significant too (P < 0.01) but of minor importance. Therefore, environmental stability of varieties should be a major breeding goal. The varieties Solitar, History and Florett were most resistant and stable as revealed by a regression approach, and the susceptible varieties were generally unstable. Hence, STB resistance and stability are correlated (P < 0.01), but there were some exceptions (Tuareg, Ambition). Promising candidates for an environmentally stable, effective adult-plant resistance have been identified.

Bacillus megaterium shows potential for the biocontrol of septoria tritici blotch of wheat

Control of septoria tritici blotch (STB) of wheat caused by the fungal pathogen Mycosphaerella graminicola is heavily reliant on fungicide application. Rapid emergence of fungal isolates resistant to Quoine outside Inhibitors (QoI) and with reduced sensitivity to triazole-based fungicides necessitates the development and adoption of alternative control strategies. A collection of bacteria originating from barley leaves and grain, oat chaff and wheat rhizospheres and leaves were screened for their ability to control STB. A total of seven bacteria were further assessed under controlled environmental conditions and these inhibited STB development by up to 92%. Three of these bacteria [ Pseudomonas fluorescens (strains MKB21 and MKB91) and a Bacillus megaterium (strain MKB135)] were assessed for their abilities to control STB on adult wheat plants in small-scale field trials, conducted both in 2004 and 2006. In these trials only B. megaterium (strain MKB135) consistently retarded STB development (by up to 80%). Additional in vitro seedling studies showed that both B. megaterium cell wall components and its culture filtrate and P. fluorescens strain MKB91 culture filtrate were capable of inhibiting disease development (by 62, 36 and 52%, respectively). While none of the three bacteria directly inhibited fungal growth in dual culture plate assays, in dual liquid culture assays volatiles produced by these bacteria reduced fungal biomass production by ⩾43%. Thus the ability of the most promising bacterium, B. megaterium strain MKB135, to reduce STB severity may be the result of a combination of different mechanisms.

Quantification of the effects of Septoria tritici blotch on wheat leaf gas exchange with respect to lesion age, leaf number, and leaf nitrogen status

Quantification of the damaging effects of pathogens on diseased plants and inclusion of these damaging functions in crop simulation models is of great importance for a more complete understanding of yield response to diseases. In this study, the effect of Septoria tritici blotch (STB) on net photosynthetic and dark respiration rates of wheat flag leaves was quantified. Bastiaans' model: Y=(1-x)beta was used to characterize the relationship between relative leaf photosynthesis (Y, considering Ynet and Ygross) and STB severity (with x the proportion of the diseased area). The value of beta indicates whether the effect of disease on photosynthesis is larger (beta >1), lower (beta <1), or equal (beta =1) to the proportion of visible diseased area. In the experimental conditions used here, leaf nitrogen content (in a range from 0.18 to 0.24 mg cm(-2)), and leaf number (flag and second leaves) did not significantly influence the effect of STB on leaf gas exchange. By contrast, damage depended strongly on the developmental stages of the STB lesions. STB lesions had no effect on inoculated leaves before visible symptoms appeared. Chlorotic symptoms had less effect on leaf net photosynthetic rate than could be accounted for by the visible diseased area (betanet=0.81). The effect of necrotic lesions on the leaf net photosynthetic capacity was slightly greater than that accounted for by visible symptoms (betanet=1.35). Our results suggest that the effect of the necrotic symptoms on the net photosynthesis expressed by betanet >1 is due to a combination of a decrease in the gross photosynthesis (betagross still >1) and to an increase in the dark respiration rate (betagross<betanet). Finally, it is discussed how the results could improve the prediction of crop loss caused by an STB epidemic in wheat fields.